The present invention relates to a position detection apparatus and method, and an electron beam exposure apparatus and a correction method of the imaging state of an electron beam in the apparatus and, more particularly, to a position detection apparatus and method for irradiating an electron beam onto a mark to detect the position of the mark, and an electron beam exposure apparatus having a function of irradiating an electron beam onto a mark and correcting the imaging state of the electron beam on the basis of reflected electrons or secondary electrons, and its adjustment method.
An electron beam exposure apparatus must draw a new pattern on a wafer while aligning it with the position of the pattern already formed on the wafer. For this purpose, an alignment mark pre-formed on the wafer is detected, and the new pattern is drawn with reference to the detected position.
The electron beam exposure apparatus draws a pattern by deflecting an electron beam. However, when the electron beam is deflected, the imaging state of the electron beam deteriorates due to deflection errors. For this reason, the imaging state must be corrected in correspondence with the position at which the electron beam is to be imaged upon deflection.
FIG. 20 shows the arrangement of a point beam type electron beam exposure apparatus using a beam in the form of a spot. Reference numeral 201 denotes an electron gun for radiating an electron beam. The electron gun 201 ON/OFF-controls electron beam radiation in correspondence with the pattern to be drawn. Reference numeral 202 denotes a reduction electron optical system for shaping the electron beam from the electron gun 201 into a point shape, and for projecting it onto a wafer 203 in a reduced scale; 204, a deflector for scanning the wafer by the point-shaped electron beam; 205, an X-Y stage which moves while carrying the wafer; and 206, a detector for detecting reflected electrons or secondary electrons upon scanning an alignment mark on the wafer by the electron beam.
The alignment method in the above-mentioned arrangement will be explained below. When a new pattern is to be drawn on a pattern already formed on a wafer, a linear alignment mark formed on the wafer is located by the X-Y stage 205 in the vicinity of the irradiation reference position of the point-shaped electron beam. The electron beam is scanned by the deflector 204 on the alignment mark, and reflected electrons or secondary electrons from the alignment mark are detected by the detector. The position of the alignment mark with respect to the irradiation reference position of the point-shaped electron beam is obtained on the basis of the relationship between the scanning position and the quantity of reflected electrons or secondary electrons detected upon scanning. Thereafter, the electron beam is scanned with reference to the obtained alignment mark position, and the electron beam is ON/OFF-controlled in correspondence with the pattern to be drawn, thereby drawing a new pattern on the wafer.
FIG. 21A is a plan view of an alignment mark AM formed on the wafer, FIGS. 21B and 21C are sectional views of alignment marks AM formed at different positions on the wafer, and FIGS. 21D and 21E show alignment signals which represent the quantities of reflected electrons or secondary electrons detected upon scanning the alignment marks AM shown in FIGS. 21B and 21C. Note that the arrows in FIGS. 21A to 21C show the scanning direction of the electron beam.
As shown in FIGS. 21B and 21C, the sectional structures of the alignment marks AM differ depending on their positions on the wafer, formation method, and the like. Also, the coating states of a resist that covers the alignment marks AM differ depending on the positions of the alignment marks AM on the wafer and their sectional structures, the structures of patterns near the alignment marks AM, and the like. Accordingly, alignment signals that detect the alignment marks differ in units of alignment marks AM to be detected. Also, random noise from a disturbance and the detection system itself is superposed on the alignment signals. For this reason, errors are produced in the detected positions of the alignment marks.
The method of correcting the imaging state of the electron beam in the above-mentioned arrangement will be explained below. FIG. 22A is a plan view of a linear reference mark SM, FIG. 22B is a sectional view of the reference mark SM, and FIG. 22C shows a mark signal as the quantity of reflected electrons or secondary electrons detected upon scanning the reference mark SM. Note that the arrows in FIGS. 22A and 22B indicate the scanning direction of the electron beam.
In order to correct the imaging state of the electron beam, as shown in FIGS. 22A and 22B, the reference mark SM is scanned by the electron beam, and reflected electrons or secondary electrons from the reference mark SM upon scanning are detected by the detector 206. FIG. 22C shows the mark signal as the output from the detector 206. Imaging state correction data for correcting the imaging state is obtained based on this mark signal, and the characteristics of the reduction electron optical system 202 are corrected on the basis of the imaging state correction data in correspondence with the position at which the electron beam is to be imaged upon deflection.
However, signal components of the mark signal are small and, hence, the ratio of noise is large (poor S/N ratio), as shown in FIG. 22C. When the electron beam is focused to draw a micropattern, the signal components of the mark signal become smaller, and the influence of noise becomes larger. Accordingly, a demand has arisen for a method that can appropriately adjust the imaging state by improving the S/N ratio of such a mark signal.